This invention relates to restoring selectivity of cracking catalysts which are contaminated with metals during catalytic cracking operations. The term selectivity herein refers to conversion of the feed to desired gasoline range hydrocarbons. Corollary to increased selectivity is decreased production of coke and hydrogen.
Conventionally catalytic cracking processes are used to crack heavy hydrocarbon feedstocks to produce gasoline and light distillate fractions and in which process there is no net consumption of hydrogen. Metals typically present in the feedstock, such as nickel, vanadium and iron tend to deposit on and contaminate the catalyst resulting in deterioration of its selectivity, which thereby results in decreased gasoline production. Further, the contaminant metals tend to increase undesirable coke production and to increase undesirable secondary cracking as manifested by an increase in hydrogen production.
The use of boron is known in the original preparation of catalysts suitably employed for cracking of heavy hydrocarbons; see e.g., U.K. Pat. No. 1,313,174 and Netherlands patent application No. 7614020. Additionally, boron is disclosed as a promoter for a variety of crystalline alumino-silicate catalysts in e.g., U.S. Pat. Nos. 3,293,192; 3,328,119; 3,346,512; 3,740,347; 3,758,538; 3,072,563; 3,803,026 and 4,029,716. However, no patents have been found disclosing the use of boron for restoring the selectivity of metals contaminated cracking catalyst.